1. Field of the Invention
The present invention relates to an optical disk device, which is enabled to record and/or read data by irradiating an optical disk with a light and, more particularly, to an optical head for irradiating the optical disk with a light.
2. Description of the Related Art
In recent years, a medium for recording images, voices or information has been mostly exemplified by an optical disk, which can-record and/or read when irradiated with a light. The CD (Compact Disc), the DVD (Digital Versatile Disc) and so on are widely used as the optical disk. An optical disk device for recording and/or reading the data in/from the optical disk as the recording medium is provided with an optical head for irradiating the recording face of the optical disk with a laser beam and detecting the light reflected.
FIG. 1 is an arrangement diagram of the optical head. As shown in FIG. 1, the optical head includes a laser beam source Ld, a mirror Mr, a collimator lens Lc, an objective lens Lb, a beam splitter Bs and a light receiving element Pd. The laser beam, as emitted from the laser light source Ld, partially transmits through the beam splitter Bs, and is reflected by the mirror Mr into the collimator lens Lc. The laser beam having entered the collimator lens Lc is projected as a parallel beam into the objective lens Lb. The laser beam having entered the objective lens Lc irradiates the recording face of an optical disk Ds.
At this time, the laser beam is focused on the recording layer of the optical disk Ds and is emitted such that the optical axis and the recording layer of the optical disk Ds are normal to each other. The beam splitter Bs is a prism for transmitting and reflecting the incident laser beam by half and for introducing the laser beam reflected by the optical disk Ds into the light receiving element Pd. This light receiving element converts the light into an electric current so that the data is read out according to the intensity of light.
FIG. 8 is a top plan view of an optical head of the related art, and FIG. 9 is a sectional view of an actuator shown in FIG. 8. An optical head C, as shown in FIG. 8, is provided with a slide base 91 for supporting the collimator lens Lc, and an actuator 92 for driving the objective lens Lb. The slide base 91 is provided, on its upper face, with ball seats 911 for forming a large common spherical face, and, on its side face, with a shaft 912 formed for regulating the action of the optical head C in a disk track direction (or a disk radius direction), a sliding hole 913 slidably engaging with the shaft 912, a rack 914 formed adjacent to the sliding hole 913, and a pinion 915 meshing with the rack 914.
The actuator 92 includes the objective lens Lb, a lens holder 93 for holding the objective lens Lb, and an actuator base 94 for supporting the lens holder 93.
The lens holder 93 includes: a lens holding unit 931 for holding the objective lens Lb; a shaft hole 932 for fitting the later-described shaft 943 of the base 94 slidably and rotatably therein; a tracking coil 933 for rocking the lens holder 93 around the shaft 943; a focusing coil 934 for sliding the lens holder 93 along the shaft 943; and a magnetic plate 935 for receiving a magnetic force generated by the later-described permanent magnet disposed in the actuator base 94.
The actuator base 94 includes: a bottom face 941 having a rectangular shape in a top plan view; rising walls 942 rising from the four sides of the bottom face 941; the shaft 943 protruding from the bottom face 941 into the case; a permanent magnet 944 rising across the shaft 943 and arranged to confront the rising walls 942; and protrusions 945 formed on the back side of the bottom face 941 and having their leading ends formed into ball faces to contact with the ball seats 911 of the slide base 91. The actuator 92 is placed such that the protrusions 945 of the actuator base 94 can slide on the ball seats 911 of the slide base 91. The shaft 943 is made of a magnetic material so that a magnetic field is generated between the permanent magnet 944 and the shaft 943.
The shaft 943 is so arranged in the actuator base 94 as to be rotatably and slidably fitted in the shaft hole 932 of the lens holder 93. At this time, the magnetic plate 935 of the lens holder 93 is arranged in the magnetic field which is established between the permanent magnet 944 and the shaft 943. The magnetic plate 935 is arranged in the magnetic field so that the magnetic force is applied to the magnetic plate 935. The lens holder 93 is supported in such a floating state by the magnetic force applied to the magnetic plate 935 that it may not contact with the actuator base 94.
The Lorentz's force is generated in the tracking coil 933 by feeding the electric current to the tracking coil 933. The lens holder 93 is rocked on the shaft 943 by this Lorentz's force. When the focusing coil 934 is fed with the electric current, on the other hand, the Lorentz's force is generated in the focusing coil 934. The lens holder 93 is slid by this Lorentz's force in the axial direction of the shaft 943.
As shown in FIG. 8, the actuator base 94 is fixed on the slide base 91 by fastening its three portions with screws 95, although not limited thereto. The screws 95 for fixing the actuator base 94 are so arranged to hold the orthogonal portions of the actuator base 94 having the rectangular shape in a top plan view, that one screw 950 is disposed near one corner whereas two screws 951 are so disposed at another corner as to interpose the same corner.
The single screw 950 is equipped with a spring 96. The actuator base 94 is biased toward the slide base 91 by the elastic force of the spring 96. The actuator base 94 receives the elastic force from the spring 96 mounted on the screw 950, and the curved faces of the protrusions 945 are moved in contact with the curved faces of the ball seats 911 by fastening or loosening the two screws 951 so properly that the protrusions 945 may slide and rotate on the ball seats 911. Thus, the actuator 92 can change its inclination smoothly with respect to the slide base 91. By adjusting the angle of the actuator 92 with respect to the slide base 91, the inclination of the optical axis of the laser beam projected from the objective lens Lb can be adjusted to irradiate the recording face of the optical disk Ds normally (refer to JP-A-8-161756).